From this formula, you can see that there is a decreasing gain rate (due to the natural log) per point you put into hero attack.

Some sample values of % damage gains for some values of x:

1-2 results in 3.5% increased damage

40-41 results in 1.25% increased damage

99-100 results in 0.6276% increased damage

So the question you should ask yourself is, will a single point of hero damage give me a bigger boost than a single upgrade of weapon damage? (The answer is almost always no).

For instance, even if your weapon damage caps out at an upgrade of 50 damage (weapon upgrade cap is a factor of base weapon damage, just using 50 as an example), your base weapon damage would have to be over 4000 in order to make it worth putting 1 point into hero damage to push your stat from 40-41. Since most heros who focus on damage already have some super high hero damage stats, your weapon damage would have to be insanely high to even consider it.

Using the 50 upgrade cap as an example again, if your hero has a hero damage stat of 150, your weapon would have to do more than 11233 damage before you should put 1 point into the hero damage stat.

Graph Pic There is simple graph that use wiki an @yx. formula. Lines give you weapon damage increase in percents. X-axis is current stat. Y-axis is overall damage percentile increase. Black lines is for increasing stat by 1, blue by 10, and red by 20. Diminishing returns is very noticeable. Bear in mind that this is value for one hit. Multiple hits give more dps. As example see countess and squire finishing hits. In summary this is absolutely right weapon damage is full coefficient when hero damage is under natural logarithm.
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aardvarkApr 4 '12 at 12:05

It depends on how much Hero Damage you have, like with most other Hero/Tower stats you have diminishing return on the stat where Weapon damage is a direct multiplier, so the lower your Hero damage is the more bonus you will get from gaining more Hero Damage, where Weapon damage is a constant increase in damage.

Here is a graph from dungeon defenders wiki showing the original 4 classes multiplier compared to points in Hero Damage(I believe Squire and Hunter have same multiplier and you can't see the Squire because the hunter is right on top).

My personal recommendation when upgrading weapon is to make sure the weapon have a good base damage so you can get maximum out of upgrading it's damage and it should have good bonus to Hero Damage and preferably also other important stats before upgrading and then place all upgrades on a weapon in to number of shoots > speed > weapon damage.

The reason for the need of good base damage is due to when upgrading a weapons damage the amount it goes up is a % base of existing damage until it reaches a cap, so it is preferred that it is already at needed damage to reach cap when upgrading at level 1. You can do some calculations using this spread sheet (make a copy of it and you can edit the values).